Various kinds of electronic apparatuses have been developed, wherein personal computers and television receivers are able to incorporate radio interfaces using a wireless local area network (LAN), WiMAX®, ultra-wideband (UWB), Bluetooth®, and the like to download content and various kinds of data from Web sites and the like via the radio interfaces.
The antenna device used in the above radio interface generally includes two antennas to obtain a diversity effect. For this reason, when an electronic apparatus is to accommodate an antenna device, the device needs to ensure a wider accommodation space than when using one antenna. On the other hand, an electronic apparatus such as a personal computer has a limited surplus space in the housing due to a reduction in the thickness of the housing and high-density packing of circuit components. For this reason, when accommodating an antenna device in an electronic apparatus, the two antennas are inevitably located close to each other. If, however, the two antennas are close to each other, the interference between the antennas becomes large. This may lead to inability to obtain desired antenna performance.
Under the circumstances, there has been proposed an antenna device which provides a notch in a ground pattern at a position between the two antennas to prevent the propagation of a high-frequency signal between the antennas. There has also been proposed an antenna device which provides slits, respectively, at positions on a ground pattern which correspond to the two antennas and also provides a stub at a position on the ground pattern which corresponds to the symmetry axis between the two antennas so as to reduce mutual coupling between the antennas.
These conventionally proposed antenna devices each are configured to cancel out high-frequency currents transmitted between the feed terminals of the two antennas by using an open stub. This makes it necessary to form, in the ground pattern, a notch, slit, and the like whose dimensions are strictly defined, leading to the need to take time and effort for processing and a complicated, large-sized structure. In addition, when wiring feed cables and the like, the notch provided in the ground pattern may be short-circuited, resulting in a deterioration in reliability.